The maximal full expiratory maneuver measures expired volume (FEV1) and flow following deep inhalation. In contrast,a maximal partial expiratory maneuver expiration starts at lower lung volume thus avoiding the need for deep inhalation,which may alter the true effect of bronchodilators on expiratory flow by inducing bronchodilation or bronchoconstriction. We therefore hypothesize that maximal partial expiratory flow (MEFP) is a more sensitive measure of bronchodilator response than maximal full expiratory flow (MEFF) and FEV1. To test this hypothesis, we compared the change in expiratory flow measured by MEFP and MEFF in response to cumulative doses of inhaled albuterol.
This was an open-labeled study in which we enrolled 18 subjects (8 normal, 5 with stable asthma and 5 with stable COPD). Each subject underwent measurements of lung mechanics including inspiratory and expiratory lung resistance (Rli and Rle), lung volumes (TLC) and FEV1. In addition expiratory flows were measured at 30% of vital capacity using MEFP and MEFF (Vp30 and Vm30, respectively). Serial measurements were obtained; at baseline, 20 minutes following the administration of inhaled placebo and cumulative doses of albuterol (180, 360, and 540 micrograms). ANOVA was used to compare responses, a p < 0.05 was considered as statistically significant.
FEV1, Rli, Rle, Vp30 and Vm30 improved in all subjects following bronchodilator administration (comparing baseline to maximum albuterol dose). However, only Vp30 was able to to identify changes at each level of bronchodilator administration (p < 0.05).
Our data suggest that MEFP is more sensitive than MEFF and FEV1 in detecting expiratory flow improvement in response to cumulative doses of inhaled albuterol.
MEFP provides a sensitive method to measure the bronchodilator response in patients with expiratory flow limitation. This measurement may be useful in determining the optimal bronchodilator dose in patients with asthma or COPD.
A. Sharafkhaneh, None.